1. Field of the Invention
This invention relates to a hydraulic circuit, especially for a clutch. More particularly it relates to an emitter device which is adapted to transmit an order for control to a receiver device through a hydraulic path.
2. Description of the Related Art
Such apparatus is known conventionally under the name of a master cylinder. In a traditional configuration, the master cylinder comprises two main parts which are, firstly, a piston and cylinder assembly in which the piston is actuated by a pedal, for example a clutch pedal, and secondly, a hydraulic fluid reservoir which is adapted to compensate for the variations in volume in the fluid due to wear in the clutch liners or due to possible leaks in the hydraulic circuit.
Apparatuses of this kind are for example described in the document FR-A-2 522 757. In general terms they comprise, between the reservoir and the hydraulic chamber defined by the cylinder and in which the piston is displaceable, a non-return means which enables the circuit to be refilled in its rest position and enables the circuit to be put under pressure.
In these traditional apparatuses, the seals which provide sealing of the pressure chamber often consist of a seal carried by the piston or, as in the above mentioned document, a flexible membrane which is disposed between the piston and the cylinder; the central portion of this membrane, which is fixed to the cylinder by its periphery, follows the longitudinal displacements of the piston during engagement and disengagement of the clutch. These seals are subjected on one of their faces to a fluid environment, and on their other faces to an atmospheric environment which results in a dry and often polluted surface. This difference in environment, and the action of pressure, leads to a relatively limited useful life of these seals, which is the source of leaks that are potentially dangerous, in this case for the user of the vehicle.
Receiver devices, located at the end of the hydraulic circuit, for example in line with the clutch release bearing, operate and are designed in principle substantially identically to those of the emitters. They naturally have the same problems in practice in the traditional technology.